(1) Technical Field
This invention relates to a diaphragm circulator and, more generally, to a device whereby mechanical power is converted into hydraulic power, i.e., the product of the flow rate multiplied by the pressure, for a liquid or gaseous fluid charged or uncharged with particles, or for any material capable of flowing (divided, powdery, fluidized or emulsified materials).
(2) Description of the Prior Art
There are numerous types of pumps, suction devices, compressors, fans . . . which perform this function. A new technique has recently appeared for providing this function, at least for a liquid, by means of a diaphragm acting as an intermediate means of converting (a transfer medium) mechanical power (the integral over a time interval of the product of force multiplied by displacement) into hydraulic power (the integral over the same interval of the product of flow rate multiplied by pressure), this transfer occurring by way of a deformation and kinetic energy of this diaphragm, the deformation being propagated in the diaphragm in the form of a ripple and the corresponding energy being progressively transferred to the fluid with which the diaphragm is in contact.
The document EP 880 650 exemplifies several embodiments of such a fluid circulator while emphasizing certain requirements to be met for there to be an efficient transfer of energy between the diaphragm and the fluid, resulting in an increase in the hydraulic power of the fluid. These requirements are the establishment of tension in the diaphragm in order for there to be ripple propagation, on the one hand, and, on the other hand, the presence of means of creating a damping of the ripple amplitude during the progression thereof from an edge of the diaphragm, where this ripple is generated by a mechanical actuator, up to an opposing edge.
This document teaches the use of rigid walls as damping-creating means, the spacing of which decreases from the inlet port to the exhaust port for the fluid treated by the circulator.
Many studies have been conducted on this new device in order to better characterize the phenomena involved, which had never before been explored, and to optimize the parameters which govern these phenomena. In particular, these studies made it possible to better identify the requirements to be met, which are stated to a limited extent in the document EP 880 650, which furthermore is the only element exemplifying the prior art for this new technique.
This is how experiments showed that the tension state of the diaphragm is a variable which is correlated with the mechanical properties of the material of this diaphragm. In reality, the initial tension state of the idle diaphragm can be equal to zero if, for example, the diaphragm is made of a material which is elastically deformable in at least one direction, combined with a geometry such that imposing a deformation on the diaphragm produces tension therein, in the aforesaid direction, which enables progression of this deformation in the form of a ripple, along this direction, which becomes the direction of propagation. Hereinafter, this type of diaphragm will be referred to as a diaphragm having intrinsic tension-creating means. For example, this will involve an elastic disk-shaped diaphragm, with or without an opening at the centre, wherein the outer edge remains undeformed during the excitation thereof by the actuator, while the idle diaphragm is not tensed. It may likewise involve a flat elastic diaphragm wherein the two ends are subjected to forces which oppose the forces imparted to the diaphragm by the fluid in which the energy is transferred. Owing to the presence of these forces, the conditions necessary for the propagation of a deformation produced at one end towards the other end are present.
It was also observed that a diaphragm consisting of a sheet which is flat when idle, non-deformable under tension, in the directions of the plane thereof, but elastically deformable under bending, e.g., about an axis contained within this plane, constitutes a medium enabling operation like a diaphragm according to the invention, if the diaphragm is subjected to a tensile or simply holding force perpendicular to or having a component which is perpendicular to the axis about which the bending occurs. This perpendicular direction is the direction of propagation.
Furthermore, theoretical and experimental research made it possible to clarify that it was possible to create a forced damping of the ripple amplitude without necessarily having to decrease the spacing of the stationary walls between which the diaphragm ripples. As a matter of fact, an excitation of the actuator resulting in the application of an reciprocating force or an reciprocating couple of given frequency and amplitude forces, at an edge of the elastic diaphragm placed inside the fluid, in the absence of walls surrounding it, generates ripples capable of propagating along the diaphragm towards the side thereof which is opposite the excited side, with a free amplitude which may be characterized by envelope surfaces of this amplitude. In order to visualize these envelope surfaces, a reflectionless propagation of waves or ripples considered, i.e., in the (theoretical or virtual) case where the diaphragm is of infinite length or the evolution of the amplitude of a primary ripple between a first instant, after the creation thereof, and a second instant separated from the first by a relatively short time interval, considering the dimensions of the diaphragm. The shape of these surfaces depends on the nature of the excitation of the diaphragm edge. Thus, in the case of excitation by means of an actuator which moves the edge of the diaphragm, the envelope surfaces will have a divergent bell-shaped profile; in the case of an actuator transmitting a couple of forces to the edge of the diaphragm, the surfaces will instead have the profile of two curves secant to the axis about which the torque is transmitted. Force damping of this ripple is obtained if stationary walls between which the diaphragm ripples are placed between (inside of) these envelope surfaces.
This condition does not necessarily eliminate a decrease in their spacing, as is described in the document EP 880 650. For particular diaphragm geometries and types, and particularly in a gaseous fluid, it is indeed possible to observe that the envelope curves diverge between the excited edge and the opposite edge of the diaphragm, thus, by simply reducing the degree of divergence, hydraulic power is successfully transferred into the fluid. The greater this reduction, the greater the preference given to the pressure component in this energy. The type of material comprising the diaphragm as well as the uniformity thereof, or the lack of uniformity thereof, in the direction of progression of the ripples, are also determining factors in the shape of the envelope surfaces of the amplitude of a ripple during the propagation thereof into the diaphragm, and are therefore determining factors in the shape and relative spacing of the rigid walls which create the forced damping of this ripple. In particular, for a uniform diaphragm, it is advantageous to provide for the thickness thereof to decrease in the direction of propagation of the ripples. The envelope curve of a tapered diaphragm such as this is more divergent than for a diaphragm of constant thickness, all things being otherwise equal. Due to this diaphragm geometry, a high damping factor is obtained, since stationary walls can be well within these envelope curves.